Abstract This paper deals with the performance of delay-sensitive applications
running over a network that offers multiple classes of service, where the
adaption of application rates in response to network feedback is the primary
mechanism available for controlling quality of service. We first evaluate the
gain in utilisation allowed by the introduction of several classes of service. To
this end we compare the pairs of achievable rates, or schedulable regions, for
two types of applications with two distinct delay requirements that make use of a
single resource, with either no differentiation, simple priority-based
differentiation, or earliest-deadline-first (EDF) scheduling-based
differentiation. The main observations are that the gain achieved by
differentiation is essentially affected by traffic burstiness, and that the two
differentiation schemes yield very similar performance. We then consider what
feedback information should be sent to traffic sources from different classes,
casting the problem in the framework of optimisation-based congestion control. We
establish a connection between the sample-path shadow price rationale for
feedback synthesis and the rare perturbation analysis technique for gradient
estimation in discrete event systems theory. Based on this connection, we propose
several marking schemes, for simple priority-based differentiation with a measure
of cost based on loss or delay, and also for EDF-based differentiation with
loss-based cost. The interaction of these marking algorithms with simple
congestion control algorithms is studied via simulations